1. Field of the Invention
The present invention relates to image processing of an electronic camera capable of partially reading out image signals from an image pickup device.
2. Description of the Related Art
An electronic camera which partially reads out any random partial image area from a maximal image area of an image pickup device and generates image data is conventionally and publicly known. For example, Japanese Unexamined Patent Application Publication No. Hei 9-135388 (paragraph [0187] and FIG. 52) discloses a technique of removing fixed pattern noise caused by a dark current component in the electronic camera capable of partial readout from the image pickup device.
However, image processing (such as line crawling correction, luminance shading correction, gain correction, gamma correction, color matrix calculation, or the like) with a conventional electronic camera was performed with a parameter based on a characteristic of the partial image area in partial readout, with no consideration given to characteristics other than that of the partial image area. Accordingly, if the same subject is photographed under the same photographing condition in partial readout and all pixel readout, a partial image subjected to the image processing in the partial readout and an entire image generated in the all pixel readout would differ and give the photographs a sense of incongruity.
If the partial image is generated by being cut out of the entire image, the above incongruity between the partial image and the entire image is resolved. However, in this case, the entire image needs to be generated with the all pixel readout in order to generate the partial image. This is inefficient since this would drastically increase the processing time required to generate the partial image. Moreover, the technique in Japanese Unexamined Patent Application Publication No. Hei 9-135388 merely stores beforehand the data on fixed pattern noise in an area wider than the partial image area to prevent the data from being re-fetched. This is done as a measure for preventing reduction of frame rate for when the partial image area is changed. Accordingly, the technique in Japanese Unexamined Patent Application Publication No. Hei 9-135388 does not resolve the above-described problem at all.